1. Field of the Invention
This invention pertains to injection of spin polarized electrons into a nonmagnetic material at room temperature and in absence of an external magnetic field.
2. Description of Related Art
The relatively new field of spin electronics or spintronics is based on the spin of an electron rather than its charge, as is the case for all conventional electronics.
The spin of an electron has been mainly ignored, although it represents a powerful new way to build electronic devicesxe2x80x94spintronics. Instead of controlling the flow of charge, spintronic devices operate by manipulating both direction of the spin and the electron charge. Potential for spintronics is not only for very high speed, very low power systems for computation and communication, but for some applications which have not yet been conceived.
Some major discoveries have been made recently that will revolutionize electronics of the future. A very long lived collective and coherent spin state has been formed by shining circularly polarized light on conventional semiconductors like silicon, gallium arsenide, gallium nitride, etc. In addition, ferromagnetism was discovered in GaMnAs at 120 K, which opens the door to even higher temperature ferromagnetic semiconductors.
The combination of new discoveries will make new paradigms of spintronic devices for opto-electronics and very high performance logic, memory and perhaps quantum computation and communication on more traditional materials than the spintronic devices.
Coherence has been observed to persist over hundreds of nanoseconds and for distances of hundreds of microns. This indicates that this coherent state can be utilizes to carry and process the spin information which may be the basis for a new paradigm in electronics. An experiment performed on a nanoparticle quantum dot indicates that a coherent spin state consisting of a very few electrons can persist for long times in these nanostructure quantum dots even at room temperature.
One of the major challenges of semiconductor spintronics is the ability to transfer spin information across boundaries between different semiconductors. A recent experiment illustrates that in the case of a GaAs/ZnSe boundary, the transfer process proceeds without much difficulty and spin dependent information is transferred across quickly and with high fidelity. Such an experiment can lead the way to a more complete understanding of the spin dependent properties of semiconductors.
There are three areas that will definitely be impacted by spintronics. The first is Quantum Spin Electronics, which refers to devices that are more conventional but can be enhanced by adding the spin degree of freedom to their operation. Such devices include spin transistors, spin-LEDs, spin-resonant tunneling diodes and perhaps even spin lasers. The second area is Coherent Spin Electronics and it takes advantage of the special coherence that was discovered recently. In this second case, devices that might be built are optical switches, encoders, decoders, modulators, phase logic and perhaps phase memory. The third and final area is Quantum Information Processing and involves using the coherent spin state to perform quantum mechanical operations for the exotic field of quantum computing and quantum communications, perhaps enabling something like a quantum internet in the no-too-distant future.
The invention disclosed and claimed herein is believed to pertain mostly to the first area identified as Quantum Spin Electronics.
Room temperature transfer of spin polarized electrons with efficiency of about 2% is exemplified in literature articles by P. R. Hammer et al in Phys. Rev. Lett. 83, 203 (1999); by S. Gardalic et al in Phys. Rev. B 60, 7764 (1999); and by H. J. Zhu et al in Phys. Rev. Lett. 87, 016601 (2001). Transfer of spin polarized electrons in an external magnetic field and at very low temperature of about xe2x88x92270xc2x0 C. with efficiency exceeding 50% is exemplified in literature articles by R. Fiederlins et al in Nature 402, 790 (1999); by Y. Ohno et al in Nature 402, 790 (1999); and by B. T. Jonker et al in Appl. Phys. Lett. 77,3989 (2000).
An object of this invention is the injection, at room temperature and in absence of an external magnetic field, of spin polarized monochromatic (same energy) electrons of a particular magnetic moment from a ferromagnetic electrode through a nanocrystal doped with a paramagnetic ion and into a nonmagnetic electrode, with applied voltage between the ferromagnetic and the nonmagnetic electrodes.
Another object of this invention is the control of injection of spin polarized electrons from a ferromagnetic to a nonmagnetic materials, this control includes enhancing or suppressing injection thereof and changing sign of the spin injection coefficient which equals to the ratio of the difference between currents of electrons with spin up and spin down projections to the sum of these currents.
Another object of this invention is alignment of the magnetic moment of the paramagnetic ion residing in the nanocrystal as a result which, the doped nanocrystal acts as a spin filter to pass only an electron with a particular spin projection, thus either enhancing or suppressing spin polarization of the current.
Another object of this invention is the injection of spin polarized electrons at room temperature and in absence of an external magnetic field.
Another object of this invention is the filtering of the spin polarized electron current with efficiency of up to 100%, which can result in enhancement of up to several times in the spin injection coefficient relative to that in the absence of the doped nanocrystal.
These and other objects of this invention can be attained by a device and a method for injecting spin polarized electrons. The device includes spaced ferromagnetic and nonmagnetic electrodes with a nanocrystal doped with a single paramagnetic ion disposed between and connected with the ferromagnetic and nonmagnetic electrodes by tunneling contact, with leads between the electrodes for applying voltage. The method for injecting spin polarized electrons at room temperature and in absence of an external magnetic field includes the step of transferring spin polarized electrons under influence of applied voltage from a ferromagnetic electrode, into nanocrystal doped with a single paramagnetic ion and finally, from the doped nanocrystal into a nonmagnetic electrode.